The present invention relates generally to metal cutting tools and more particularly to a countersinking tool having removable cutting inserts.
Conventional countersinking tools for countersinking relatively large holes (e.g., one inch or larger in diameter before the countersinking operation) generally comprise a monolithic, unitary tool having six or seven integral cutting edges machined or ground into the tool along a downwardly tapering, frusto-conical portion of the tool. Each cutting edge is ground with a predetermined rake which is the angle defined by the two surfaces which converge to form the cutting edge. The particular angle or rake ground on the edge depends upon the material which is to be cut by the cutting edge. Different materials (e.g., different metals) require different rakes for optimum cutting thereof. Similarly, for a given material, such as steel, different hardnesses thereof require different rakes for optimum cutting.
A conventional countersinking tool, with the cutting edges constituting an integral part thereof, may have cutting edge rakes which are optimum for one given material but which are less than optimum for another given material, and, to provide optimum cutting on the other given material, the cutting edges must be changed. For conventional countersinking tools with integral cutting edges, this means removing the entire countersinking tool from the machining head which imparts rotation to the tool and replacing it with another countersinking tool having integral cutting edges with the desired rakes.
Because it is not convenient to change the countersinking tool every time a different rake is required, it is not unusal for a countersinking tool to be used indiscriminately, regardless of the rake which happens to be ground into the integral cutting edges and regardless of the material which is undergoing countersinking. In order to perform an adequate cutting operation under these circumstances, it is necessary to provide the countersinking tool with six to eight cutting edges.
Moreover, when the integral cutting edges on a conventional countersinking tool wear out, the entire countersinking tool must be subjected to a regrinding operation which is a relatively complicated, time-consuming and expensive operation. This regrinding operation must be performed on a special machine which will accommodate the entire countersinking tool. Similarly, to change the rake on the integral cutting edges of the tool requires removing the entire tool from the machining head and regrinding the cutting edges using the special machine described in the preceding sentence.
The cutting edges on a countersinking tool can be reground only a limited number of times. Eventually, the edges can be reground no more and, in the case of a conventional countersinking tool with integral cutting edges, the entire tool must be thrown away and replaced, a procedure which is relatively expensive.